llvm-project/clang/test/CodeGenCXX/wasm-em-eh.cpp

// RUN: %clang_cc1 %s -triple wasm32-unknown-emscripten -fexceptions -fcxx-exceptions -emit-llvm -o - -std=c++11 2>&1 | FileCheck %s

// Test code generation for Wasm's Emscripten (JavaScript-style) EH.

void noexcept_throw() noexcept {
  throw 3;
}

// CATCH-LABEL: define void @_Z14noexcept_throwv()
// CHECK:       %[[LPAD:.*]] = landingpad { ptr, i32 }
// CHECK-NEXT:                    catch ptr null
// CHECK-NEXT:  %[[EXN:.*]] = extractvalue { ptr, i32 } %[[LPAD]], 0
// CHECK-NEXT:  call void @__clang_call_terminate(ptr %[[EXN]])
[WebAssembly] Generate __clang_call_terminate for Emscripten EH (#129020) When an exception thrown ends up calling `std::terminate`, for example, because an exception is thrown within a `noexcept` function or an exception is thrown from `__cxa_end_catch` during handling the previous exception, the libc++abi spec says we are supposed to call `__cxa_begin_catch` before `std::terminate`: https://libcxxabi.llvm.org/spec.html > When the personality routine encounters a termination condition, it will call `__cxa_begin_catch()` to mark the exception as handled and then call `terminate()`, which shall not return to its caller. The default Itanium ABI generates a call to `__clang_call_terminate()`, which is a function that calls `__cxa_begin_catch` and then `std::terminate`: ```ll define void @__clang_call_terminate(ptr noundef %0) { %2 = call ptr @__cxa_begin_catch(ptr %0) call void @_ZSt9terminatev() unreachable } ``` But we replaced this with just a call to `std::terminate` in https://github.com/llvm/llvm-project/commit/561abd83ffecc8d4ba8fcbbbcadb31efc55985c2 because this caused some tricky transformation problems for Wasm EH. The detailed explanation why is in the commit description, but the summary is for Wasm EH it needed a `try` with both `catch` and `catch_all` and it was tricky to deal with. But that commit replaced `__clang_call_terminate` with `std::terminate` for all Wasm programs and not only the ones that use Wasm EH. So Emscripten EH was also affected by that commit. Emscripten EH is not able to catch foreign exceptions anyway, so this is unnecessary compromise. This makes we use `__clang_call_terminate` as in the default Itanium EH for Emscripten EH. We may later fix Wasm EH too but that requires more efforts in the backend. Related issue: https://github.com/emscripten-core/emscripten/issues/23720 2025-02-27 16:23:18 -08:00			`// RUN: %clang_cc1 %s -triple wasm32-unknown-emscripten -fexceptions -fcxx-exceptions -emit-llvm -o - -std=c++11 2>&1 \| FileCheck %s`

			`// Test code generation for Wasm's Emscripten (JavaScript-style) EH.`

			`void noexcept_throw() noexcept {`
			`throw 3;`
			`}`

			`// CATCH-LABEL: define void @_Z14noexcept_throwv()`
			`// CHECK: %[[LPAD:.*]] = landingpad { ptr, i32 }`
			`// CHECK-NEXT: catch ptr null`
			`// CHECK-NEXT: %[[EXN:.*]] = extractvalue { ptr, i32 } %[[LPAD]], 0`
			`// CHECK-NEXT: call void @__clang_call_terminate(ptr %[[EXN]])`